Rapid, spatial-data viewing and manipulating including data partition and indexing

ABSTRACT

A high-density, distance-measuring laser system and an associated computer that processes the data collected by the laser system. The computer determines a data partition structure and stores that structure as a header file for the scan before data is collected. As the scan progresses, the computer collects data points until a predetermined threshold is met, at which point a block of data consisting of the data points up to the threshold is written to disk. The computer indexes each data block using all three coordinates of its constituent data points using, preferably, a flexible index, such as an R-tree. When a data block is completely filled, it is written to disk preferably with its index and, as a result, each data block is ready for access and manipulation virtually immediately after having been collected. Also, each data block can be independently manipulated and read from disk.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/968,948 filed Aug. 30, 2007, which is incorporated herein byreference in its entirety.

BACKGROUND

Laser distance-measuring systems measure space to such a high degree ofmeasurement density that the resultant mass of points, often called apoint cloud, can appear as a coherent scene in the manner of apointillist painting. Systems meeting this description include the laserscanner described in U.S. Pat. No. 5,988,862, the disclosure of which ishereby incorporated by reference, the Leica HDS6000 laser scanner fromLeica Geosystems HDS, LLC, of San Ramon, Calif., or other LIDARsystems—such as the airborne LIDAR system disclosed in U.S. patentapplication Ser. No. 11/397,246 filed Apr. 4, 2006, and incorporatedherein by reference. Each of these systems produce point clouds or setsof echoes, which are data sets representing points whose position anddistance are sensed by the system.

Typically, the systems collect data in such a way to transform rawsensor data into point data that have three position coordinates, x, y,and z. The raw sensor data is expressed in spherical coordinates: anangle θ that represents the angle of rotation about a vertical axis(shown as the z-axis in FIG. 4 of U.S. Pat. No. 5,988,862), an angle φthat represents the angle of rotation about a horizontal axis (shown asthe y-axis in FIG. 4 of the '862 patent) and a range or distance ρ. Theangle coordinates correspond with the movable laser-scanner or LIDARcomponents that determine the direction of an emitted laser pulse. Thesespherical coordinates are transformed into Cartesian coordinates, whichare more convenient for later operations on the data. Once transformed,the z coordinate corresponds to the range ρ and represents the distanceof a point from the laser scanner. (We have moved from defining thez-axis as shown in FIG. 4 of the '862 patent to the definition shown inFIG. 6A of that patent. We adhere to the definition of the x-, y-, andz-axes shown in FIG. 6A for the remainder of this specification, but oneof ordinary skill will appreciate that the label attached to theCartesian axes is arbitrary.) The aggregated z coordinates of points ina point cloud generally do not follow a predicable pattern. Indeed, thez coordinates of points are determined by the objects in the space thatthe laser system is measuring. In contrast, the x and y coordinates ofpoints follow a pattern because the laser systems—whether a laserscanner or aerial LIDAR-collect data in a regular pattern.

But using the data from three-dimensional (“3D”) laser scanners istypically a time-consuming process. Current-generation laser scannerscollect data at a rate much faster than the accompanying software canprocess it in real time. Some current laser scanners can collect data asfast as 500,000 data points per second. Near-term 3D imagers (based ongrids of collectors similar to CCDs) may soon reach 30 million datapoints per second (30 Frames/sec at 1 K×1 K points=1 M points perframe).

This produces a lot of data. Typically a 3D data point will carry alongsomewhere between 14 to 30 bytes of data depending on the resolution ofthe device and the attributes associated with each point (e.g., 12 bytesfor float precision points, 24 bytes for double precision points, 2bytes for intensity return, 3 bytes for color). Consider a14-byte-per-point baseline laser-scanner system. This system produces adata rate of roughly 7 MB/sec at a scan rate of 500 K points/sec. Giventhat disk write speeds are roughly 30 MB/see, the system already runsclose to the limits of practical data collection and storage.

After collection, the point cloud data files must usually be processedand spatially indexed for efficient use and ability to visualize thecollected data. Since the data generally is acquired in atwo-dimensional (“2D”) grid, the data is generally stored in 2D gridorder (allowing for some spaces that occur when an emitted laser pulseis never reflected back to the system and collected). To look at all thedata in 3D generally requires several days to index the data in 3D on ahigh-end desktop PC for a day's collection of points. As such, thisformat conversion generally takes significantly longer than thecollection time. This conversion is necessary for most uses of scan datasince it is typical to combine data from multiple positions to representthe scanned scene. In this usage, the 2D scan formats are practically ofno use.

BRIEF SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

One embodiment disclosed herein relates to using a computer for rapidlydisplaying and manipulating a point cloud composed of a plurality ofdata expressing three-dimensional attributes. The point cloud resultsfrom a scan with a laser system. The method includes the steps of:determining a partition structure based on the size of the point cloudand a predetermined leaf-block size; initiating the scan; adding data tomemory as it is collected until the data reaches the leaf-block size;indexing data as the data is collected, wherein indexing includesestablishing a boundary based on three-dimensional attributes of thedata; storing the boundary when the data indexed according to theindexing step reaches a predetermined node capacity; and storing thedata of the leaf-block size to form a leaf block. The partitionstructure includes a leaf-node having a leaf-node capacity substantiallyequal to the predetermined leaf-block size, and the leaf-node composesthe highest level of the partition structure, which includes at leastthe highest level and a lower level composed of at least one lower-levelnode. The predetermined node capacity is the capacity of a node in thepartition structure.

Another embodiment disclosed herein relates to using a laser-measurementdevice that collects data having three-dimensional attributes, the datahaving a regular pattern in two dimensions. The method includes thesteps of determining a partition structure for the data based on theregular pattern before initiating a scan; initiating the scan and, whilethe scan progresses, collecting the data in memory until the data fits asize criteria associated with the partition structure; writing a blockof data to disk when the data fits the size criteria; before writing theblock to disk, establishing an index based on the three-dimensionalattributes of the data; and querying the data. The index corresponds tothe block of data. Querying includes the steps of determining a spatialquery and comparing the spatial query to the index.

Additional features and advantages will be set forth in the descriptionwhich follows, and in part will be obvious from the description, or maybe learned by the practice of the teaching herein. The features andadvantages of the teaching herein may be realized and obtained by meansof the instruments and combinations particularly pointed out in theappended claims. These and other features will become more fullyapparent from the following description and appended claims, or may belearned by the practice of the invention as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent invention, a more particular description of the invention willbe rendered by reference to specific embodiments thereof which areillustrated in the appended drawings. It is appreciated that thesedrawings depict only illustrated embodiments of the invention and aretherefore not to be considered limiting of its scope. The invention willbe described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIG. 1 illustrates a laser scanner;

FIG. 2 illustrates a LIDAR system;

FIG. 3 is a flow-chart illustrating the process for storing pointsaccording to the preferred embodiment of the invention;

FIG. 4 is an illustration of scan size versus canonical blockdefinition;

FIG. 5 illustrates overlapping bounds 3D points;

FIG. 6 illustrates a flexible 3D index;

FIG. 7 is a flow-chart illustrating a process for querying 3D spatialdata according to the preferred embodiment; and

FIG. 8 illustrates the process for traversing the flexible 3D index andthe partition structure according to the preferred embodiment.

DETAILED DESCRIPTION

The principles of the embodiments described herein describe thestructure and operation of several examples used to illustrate thepresent invention. It should be understood that the drawings arediagrammatic and schematic representations of such example embodimentsand, accordingly, are not limiting of the scope of the presentinvention, nor are the drawings necessarily drawn to scale. Well-knowndevices and processes have been excluded so as not to obscure thediscussion in details that would be known to one of ordinary skill inthe art.

The principles of the present invention generally relate to a laserscanner, aerial LIDAR or other high-density, distance-measuring lasersystem and an associated computer that processes the data collected bythe laser system. The computer determines a data partition structure andstores that structure as a header file for the scan even before data iscollected. As the scan progresses, the computer collects data pointsuntil a predetermined threshold is met, at which point a block of dataconsisting of the data points up to the threshold is written to disk.The data block may be a leaf-block of the partition structure (i.e., amember of the highest level of the partition), an intermediate block orthe root block. In other words, preferably, points are collected andfilled into the appropriate blocks at every level of the partition asthe scan progresses.

The computer indexes each data block using all three coordinates of itsconstituent data points using, preferably, a flexible index, such as anR-tree. As mentioned before, when a data block is completely filled, itis written to disk preferably with its index and, as a result, each datablock is ready for access and manipulation virtually immediately afterhaving been collected. Also, each data block can be independentlymanipulated and read from a disk. It will be appreciated that anycomputer implementing the embodiments disclosed herein will includewell-known computer components such as, but not limited to, RAM andother high speed memory, a storage disk such as a hard drive or thelike, a display screen, input devices such as a keyboard and mouse, andone or more interfaces that allow the computer to transmit and receivedata.

Having generally described the principles of the present invention,attention is first made to FIG. 3, which in greater detail illustratesan embodiment disclosed herein. Initially, as shown in Step 100 in FIG.3, a computer associated with a laser system determines a partitionstructure for a scan, based on the scan size and the highest-level blocksize for the partition. It will be appreciated that the laser systemthat will perform the scan may be the laser scanner shown in FIG. 1.Additional detail regarding the laser scanner of FIG. 1 may be found inrelation to FIG. 3A of U.S. Pat. No. 5,988,862. The laser system mayalso be the LIDAR system including a LIDAR 205 shown in FIG. 2.Additional detail regarding the LIDAR system of FIG. 2 may be found inrelation to FIG. 3 of U.S. patent application Ser. No. 11/397,246. Thelaser system may also be any other suitable laser-ranging system thatcollects range data in a regular pattern in two dimensions. Note thatU.S. Pat. No. 5,988,862 and U.S. patent application Ser. No. 11/397,246have previously been incorporated by reference in their entirety.

It will be appreciated that the scan size can be determined by a userand input into the computer. Data block size may be input directly ormay be inferred from more general information that a user inputs to thecomputer. Typically, the data block size is specified as a number ofcolumns and rows of data. As will be discussed in more detail to follow,for efficient usage the preference is that the data block be square anda power of 2 (i.e., that is canonical), as this reduces memoryrequirements and computation. Of course, it will be appreciated thatnon-canonical data blocks are also envisioned by the principles of thepresent invention.

The size of the scan is typically determined by the resolution of thescan (i.e., the closeness of collected data points) and the area coveredby the scan. In a laser scanner such as the scanner disclosed in U.S.Pat. No. 5,988,862 shown in FIG. 1, the area covered by the scan may bespecified by the extent of rotation about the vertical axis of thescanner (that is, the axis perpendicular to the floor)—which with theresolution determines the number of columns of data in the entirescan—and the field of view of the scan (that is, the swath of the scanin a plane perpendicular to the floor)—which with the resolutiondetermines the number of rows in the entire scan. Likewise, it will beappreciated how these principles may be applied to additional scannerssuch as the HDS6000, to LIDAR systems such as the system shown in FIG. 2or to various other systems that collect position data in a regular way.

The computer may then determine a partition structure. This may be donebefore initiating a first laser pulse of a scan because laser systemsgenerally collect data in a regular, or almost regular, pattern intwo-dimensions. Preferably, the partition structure is set so that thetotal data collected during the scan will be partitioned as a set ofcanonical data blocks. The data blocks form the basis of lower levels ofdetail, or low-level nodes, often called leaf-nodes in many partitionstructures. The information describing such canonical data blocks isalgorithmic, whereby the computer need only store a data block indexdescribing the location of a data block on a storage disk, and need notstore a large file describing the data structure.

To more fully understand the nature of canonical data blocks, considerthe following case. Let N define the row and column size of the datablocks, which are a unit of storage in a file format (i.e., each datablock contains a grid of N×N points). The full grid row-and-column countof the entire scan is M, which is defined to be a power of two and isdivisible by N, which is also a power of two. The full row count andfull column count is set to be equal. This gives a canonical grid, whichcan be evenly subdivided into (M/N)×(M/N) leaf data blocks.

Note that in some embodiments the actual number of data points in eachdata block, or in any block composing the canonical grid, may be lessthan N×N because the extent of the scan may only partially fill someblocks as may be seen in FIG. 4. In other words, in these embodiments ifthe scan size is not a power of 2 or evenly divisible by N, the computercreates the smallest canonical structure big enough to hold the scan.This means there may be empty data points and possibly empty datablocks, but these can be represented with very little computingoverhead. Also, some points will have an intensity of zero and perhaps anull range because no valid return was received for the positionrepresented by the point.

As will be described in greater detail below with respect to FIG. 8,this canonical grid also forms the basis for a canonical partition,preferably a quad-tree partition, of a total number of levels that isequal to 1+log₂(M/N). For each level L in the quad-tree or otherpartition, a subsample version of the scan is stored, using 2^(L) by2^(L) data blocks from the next-highest level. If level zero is thelowest level (i.e., having the lowest resolution), a single 2° by 2°data block of data points results, which is an N×N point sub-sampling ofthe entire scan. At each subsequent level, each data block is subdividedinto four data blocks: so, for example, level 1 would have four 2¹ by 2¹blocks of data representing the entire scan.

The foregoing explains that the partition structure is predictable andconsistent in two dimensions because of the nature of laser system data.That is, the data points can be partitioned into data blocks based onthe two-dimensional regularity of the data points, and these data blocksare of consistent size. The data blocks themselves can be groupedtogether to form additional levels of a quad-tree or other partitionstructure.

Returning now to FIG. 3, having predetermined each node of the partitionstructure based all the scan size and data block size, the computerwrites a scan-file header, or a header for the entire scan, in Step 102.The header establishes the nodes of the partition, i.e., the index fromthe to-be-collected quad-tree data blocks, or partition data blocks, tothe storage of the block on the disk.

Next, in Step 104, the computer initiates the scan in response to userinput. The laser system begins collecting data points, which are storedin memory in Step 106 as they are collected. As mentioned earlier,several nodes of a partition at various levels in the partition may bestored in memory as data points are collected that belong in thosenodes. If a user were to see an imaginary, graphical representation ofreal-time collection of data points in memory, he or she would seeleaf-nodes filling with data points at the same time as intermediatenode. Each intermediate node having, for a quad-tree partition, an areafour times as large as any given leaf-node composing a quarter of theintermediate node, also fill with data points but more slowly and at alower density. Leaf-nodes fill first and are flushed from memory as theyare written to disk. The last node to be completed is the root node,which is written to disk when the scan is completed.

Returning again to FIG. 3, as data points are collected in memory, thecomputer in Step 109 creates a 3D index for each node. The 3D indexpreferably uses a bounding box principal such as an R-tree index,although other bounding principles may also be used. In an R-tree, eachnode contains a bound for all child nodes, and child nodes can overlap.This well suits a laser scanner, because, as shown in FIG. 5, when datais taken from a single position the bounding boxes can overlap.

FIG. 5 shows two bounding boxes 505 (solid lined box) and 506 (dashedline box), which index a data block 510 (also referred to as Block 1)and a data block 520 (also referred to as Block 2) respectively. Asshown, data block 510 is composed on data points 511, 512, 513, and 514while data block 520 is composed on data points 521, 522, 523, and 524.While each data block does not intersect the other because of theperiodic or regular nature of laser scanner data in two dimensionsdescribed previously, the 3D-Cartesian bounding boxes 505 and 506 canoverlap as shown at by the darkened area 501 because their spatialdimensions are determined as the minimum and maximum of each of the setof X, Y, and Z Cartesian coordinates of all the data points in a datablock. That is to say, the bounding box 505 has a minimum and maximum ofeach of an X, Y, and Z extent according to the minimum and maximum X, Y,and Z value for data points 511-514 and bounding box 506 has a minimumand maximum of each of an X, Y, and Z extent according to the minimumand maximum X, Y, and Z value for data points 521-524. The followingpseudo-code illustrates how the bounds are determined according to oneembodiment of the invention:

Function ExtendBounds (Bounds, Point) { If (Bounds.IsEmpty) {Bounds.Min=Point; Bounds.Max=Point; } Else { Bounds.Min.X =Min(Bounds.Min.X, Point.X); Bounds.Min.Y = Min(Bounds.Min.Y, Point. Y);Bounds.Min.Z = Min(Bounds.Min.Z, Point.Z); Bounds.Max.X =Max(Bounds.Max.x, Point.X); Bounds.Max.Y = Max(Bounds.Max.Y, Point. Y);Bounds.Max.Z = Max(Bounds.Max.Z, Point.Z); } }

Returning again to Step 109 of FIG. 3, the computer preferably generatesthe bounds for the R-tree nodes by first initializing the bounds of thedata block stored at Step 106 to empty. For each data point added to thedata block, the computer extends the bounds of the index, using acomputer-implementable version of the pseudo-code. Step 109 is performedpreferably on leaf data blocks, although the step may be performed onall data blocks (including leaf data blocks, intermediate data blocksand the root data block) or on some predetermined subset of the datablocks. The leaf data blocks may be the only blocks indexed because anR-tree index is preferably used, which is sufficiently flexible to allowconstruction of intermediate 3D-index nodes by the union of two or morehigher-level 3D-index nodes, as will be discussed in more detail tofollow. If Step 109 is performed only on leaf data blocks, thenlower-level data blocks are written to disk in Step 115 without beingfirst indexed according to Step 109.

Once a sufficient number of data points are stored to fill a data blockof the partition structure, at Step 115, the data block is written todisk or, stated another way, stored on disk. It will be appreciated thatthe laser system may not receive a return or echo for every pulse ittransmits. Even in the absence of a valid return, the computer stores apoint with a zero intensity value and a null range value, but,nevertheless, having φ, θ spherical coordinates that are transformedinto x, y Cartesian coordinates.

The entire scan need not be kept in memory, because data blocks of thescanned data are stored to disk as a data block is collected, freeing upthe memory to store the next data block. The information associated withthe data block, such as the R-tree bounds, are stored to disk with theunderlying leaf data block point data. Of course, one of ordinary skillwill appreciate that the associated information, like the R-tree bounds,may be written to disk at the end of the scan or any other time. Theimportant thing is that the information is associated with itscorresponding data block.

In some embodiments, the data blocks are stored on the disk efficiently,as shown in Step 117 of FIG. 3, in order to avoid blocking off portionsof the disk unnecessarily. As an example of the efficient storagetechniques according to such embodiments of the invention, consider atypical data block-size value N of 256. If the laser system scans 258 by254 data points (i.e., 258 columns by 254 rows), the computer would,beforehand, create a canonical grid, in which M equals 512, that is, 512columns by 512 rows, where the data actually starts at coordinate 0, 0,(as seen at 405 in FIG. 4) and empty points fill the remaining columnsand rows above the actual scanned data (i.e., column 258+, row 254+).

This generates a partition structure of two levels, such as thetwo-level quad-tree 400 shown in FIG. 4. As illustrated in FIG. 4, thereare four data blocks 410 (also referred to as “Block 1”), 420 (alsoreferred to as “Block 2”), 430 (also referred to as “Block 3”), and 440(also referred to as “Block 4”) at the highest level of the partitionstructure (i.e., Level 1). As further illustrated in FIG. 4, the blocklayout of Level 1 has two empty data blocks (block 420 and block 440),one nearly empty data block (block 430), and one nearly full data block(block 410). However, the computer will not store the empty data blocks420 and 440, and will efficiently store the partially empty data blocks,so while the quad-tree may be sparse, there is nearly no impact on diskspace.

Because the data blocks are independent, the computer can be programmedto perform as much, or as little, compression as may be desired,according to standard compression techniques. Generally speaking,compression of data blocks is desirable when compression reduces thefile size significantly, and decompressing the data read off the disk isfaster than loading an uncompressed data block.

Again returning to FIG. 3, the dashed lines indicate that Steps 112,114, and 119 are optional in some embodiments. In Step 112, prior towriting each data block to disk, the computer may optionally build a 3Dpartition or index within the data block. Preferably, if this optionalstep is performed, the index is an octree. This can be done with littleadditional overhead to compute the R-tree representation of each blockbefore writing the block to disk.

Another optional, though preferable, step is to build athree-dimensional index within the each data block, as shown in Step114. Such an index will have additional levels of spatial filtering. Tobuild such 3D index, the computer first establishes a canonicalquad-tree structure within the data block just as if the block wereitself an entire scan file such as discussed with regard to Step 112. Inother words, the leaf-blocks, for example, contain N by N points, whereN is a power of 2, so building the intra-block partition is the sameprocess as described previously with respect to Step 100 and Step 102.Likewise, the 3D index is built the same way as described with referenceto Step 109, and each node in the intra-block 3D index references agroup of data points with the data block. The group of data pointsshould preferably be indexed by rows and columns. The 3D index can bedeveloped over the quad-tree structure as deeply or shallowly asdesired. Preferably the intra-block 3D index is an R-tree. Such anR-tree index may require an additional, roughly 1% overhead storage fora 10 K by 10 K scan, where N equals 256, and a three-level R-tree indexis used with six floats per bound.

Generally, optional Steps 112 and 114 are performed for leaf-blocks, andnot intermediate blocks of the partition. However, one of ordinary skillwill appreciate that even intermediate blocks can be partitioned orpartitioned and indexed as described with respect to Steps 112 and 114.

Preferably, in Step 119, other data besides the three-dimensionalspatial coordinates of each data point are stored and associated withthe data blocks. This other data may include color, attributes, andintensity and may be independently loadable. Step 119 may be appropriatewhen certain data can be compressed more effectively as a coherent setof values of the same type. For example, intensity values can becompressed independently, where ZLIB compression can be applied to thelist of intensity values.

Though it is not shown in FIG. 3, optionally, the computer establisheslower-level, 3D-index nodes by the union of 3D index nodes overlaid onthe blocks according to Step 109. Different nodes can be formed by theunion of existing nodes, a useful feature for building a multi-levelR-tree. Preferably nodes in the 3D index correspond to nodes in thequad-tree partition.

Turning now to FIG. 6, a 3D index according to some embodimentsdisclosed herein is illustrated. In FIG. 6, an R-tree 600 consists of a3D bounds pointing to a node, which may be another R-tree node or a nodeof a partition structure 680, which is also illustrated. Bounds B0designated at 605 is the union of bounds B1, B2, B3 and B4, designatedat 610, 620, 630, and 640 respectively. To explain the concept morefully, data Blocks 615, 625, 635, and 645 (also referred to as Blocks 1through 4) in FIG. 6 are the leaf-blocks (or nodes) of the quad-tree 680according to embodiments disclosed herein. Bounds 610, 620, 630, and 640may be intermediate nodes of the 3D index that point to respective datablocks or nodes of the partition 680. The Bounds 610, 620, 630, and 640can be created according to Step 109, for example. As already mentioned,Bound 605 is created by the union of Bounds 610, 620, 630, and 640.

Returning again to FIG. 3, in Step 124, the 3D index bounds (or, in someembodiments, R-tree bounds) are stored in a scan file header. The scanfile comprises the point data for the entire scanning project or scan,as well as certain file-wide information relating to partitioningstructure. Once the data has been stored according to the embodimentsdescribed up to this point, the data is virtually immediately ready foruser viewing and manipulation as will now be described in relation toFIG. 7.

To support viewing and manipulation, the computer first reads the R-treeinformation from the scan file header, as shown in Step 200 of FIG. 7.The computer then identifies in Step 202 the partition level, preferablya quad-tree, which is appropriate to display based on the user's eyepoint and computes a spatial query for the data that will render thedata according to the eye point. To actually find the data, the computerin Step 204 traverses the index from the root, and for each child of thecurrent node, in Step 206 the computer compares or intersects the boundsof the spatial query with the bounds of the child index node, (That is,the child of the current node.)

If the intersection is empty (Yes in decision Step 208), the computercontinues to the next child of the current node, in other words, thesibling of the current node, and then conducts the intersectingoperation of Step 206 again. If the intersection is not empty (No indecision Step 208), the computer checks in decision Step 210 whether thespatial query bounds fully contain the child index node bounds. If so(Yes in decision Step 210), all data blocks within the bounds of thecurrent index node are included in the result and displayed in Step 212.Otherwise (No in decision Step 208), when the query overlaps the childindex node bounds, the computer checks whether the child corresponds toa block of data in decision Step 214. If so (Yes in decision Step 214),the data block is included in the result in Step 216. If not (No indecision Step the computer traverses down to the next level in Step 218to begin the process again.

Referring now to FIG. 8, a graphical illustration of the process of FIG.7 is shown. Assume that the point data has been partitioned into aquad-tree 900 which includes three quad-tree levels. Level 0 designatedat 910 is a quad-tree root node with point data at a low resolution whendisplayed. Level 1 designated at 920 is an intermediate quad-tree nodewith point data at a medium resolution. Level 2 designated at 930 is aleaf-node comprising leaf-blocks containing the highest resolution ofthe scan data.

An R-tree 800 also has three levels, with each level preferablycorresponding to the levels of the quad-tree 900. Bound B0 designated at810 is formed by the union of all of its child nodes and is a root node.Bounds B1 through B4 designated at 820, 830, 840, and 850 respectivelyare intermediate nodes, and can be formed by the union of any number ofchild nodes. Bound B1 (820), for example corresponds to Block 1 of thequad-tree 900 and is formed by the union of 3D indices associated withBlocks 5, 6, 7, and 8 of the partition 900. Bound B1 is formed by theunion of child nodes B5-B8, which are designated at 860, 870, 880, and890 respectively.

Of course, it will appreciated that forming Bound B1 (820) by the unionof indices associated with leaf-blocks is but one way of forming anintermediate node like Bound B1. As mentioned before, other ways includebuilding the index for Block 1 of the quad-tree 900 as Block 1 iswritten to memory in the same way the index for blocks 5, 6, 7, and 8are built according to Step 109 of FIG. 3. In other words, intermediatenodes can also be formed directly from intermediate blocks of thepartition structure, rather than by the union of indices associated withleaf-blocks of the partition. Other methods can also be employed tobuild an R-tree, all with the purpose of improving the process oflocating appropriate data blocks for viewing and manipulation.

Returning now to the example illustrated by FIG. 8, assume a user wishesto view a small portion of the scan file at high resolution, such thatthe desired data points are entirely within Block 5. To find and renderthe data points, the computer will begin at bound B0 (810), traverse tothe first child, B1 (820), and test the intersection of the spatialquery with the bounds of B1 (Step 206 in FIG. 7). Finding thisintersection to be not empty, the computer determines whether the querybounds fully contain the bounds of bound B5 (860) (Step 210). It doesnot, because the data points desired to be viewed or manipulatedspatially extend no further than the points bounded by Block 5, so thecomputer determines whether B5 corresponds to a block (Step 214). Itdoes not, so the computer traverses down to Block 5 (865) (Step 218), totest again the intersection of the spatial query bound with the boundsof Block 5 (Step 206). The spatial query is smaller than the block B5,so the intersection is not empty (according to the test at Step 208) andthe computer goes on to again query whether the query bounds fullycontain Block 5 (Step 210). They do not, so the computer determineswhether Block 5 corresponds to a data block (rather than an R-Treenode), and it does, ending the process by returning Block 5. This Block5 may be even further filtered, if desired. It will be appreciated thata similar process may be followed when the user desires to view the datapoints in block 6 (875), block 7 (885), or block 8 (895).

Having described the preferred embodiment in detail, certain additionalinformation follows. First, the granularity of the process according tothe preferred embodiment is controlled by the block size N. Iffine-grain access is common or desirable, a small value of N may beused. Second, it should be noted that each block of point data may bestored in a different coordinate system from its sibling data in thescan file. This may happen where a user collects a plurality of relatedscans and wishes to combine them into a single, large scan project. Thedata can be transformed into a common, world coordinate system accordingto well-known principles. (U.S. Pat. No. 5,988,862 discloses, amongother things, one way to register point clouds at col. 20, line 7, etseq.). The user need simply establish the coordinate transformation foreach block or set of blocks that are related by having the samecoordinate system to some world coordinate system that will be common toall of the scans in the project. By transforming the queries andresults, multiple, registered scans can be viewed in 3D.

One of ordinary skill will appreciate that each level in the partitionof the point data is independently stored and loadable. The user canaccess the level of resolution that he needs for any request, withoutaccessing all of the blocks on disk. For example, if one wants to do avery course visualization (e.g., if he is zoomed out), all he needs toload is the block from level zero. By decomposing the storage at eachlevel into N by N blocks, the computer can access each block separately,making disk access efficient.

Embodiments herein may comprise a special purpose or general-purposecomputer including various computer hardware. Portable media devices areexamples of special purpose computers. Embodiments may also includecomputer-readable media for carrying or having computer-executableinstructions or data structures stored thereon. Such computer-readablemedia can be any available media that can be accessed by a generalpurpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium which can be used to carryor store desired program code means in the form of computer-executableinstructions or data structures and which can be accessed by a generalpurpose or special purpose computer. When information is transferred orprovided over a network or another communications connection (eitherhardwired, wireless, or a combination of hardwired or wireless) to acomputer, the computer properly views the connection as acomputer-readable medium. Thus, any such connection is properly termed acomputer-readable medium. Combinations of the above should also beincluded within the scope of computer-readable media.

Computer-executable instructions comprise, for example, instructions anddata which cause a general purpose computer, special purpose computer,or special purpose processing device to perform a certain function orgroup of functions. Although the subject matter has been described inlanguage specific to structural features and/or methodological acts, itis to be understood that the subject matter defined in the appendedclaims is not necessarily limited to the specific features or actsdescribed above. Rather, the specific features and acts described aboveare disclosed as example forms of implementing the claims.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A method of using a laser-measurement device which scans in a regularpattern in two dimensions and that collects data havingthree-dimensional attributes, the data having the regular pattern in twodimensions, the method comprising the steps of: determining a partitionstructure for the data based on the regular pattern of which thelaser-measurement device scans before initiating a scan; initiating thescan and, while the scan progresses, collecting the data in memory untilthe data fits a size criteria associated with the partition structure;writing a block of data to disk when the data fits the size criteria;before writing the block to disk, establishing an index based on thethree-dimensional attributes of the data, the index corresponding to theblock of data; identifying a partition level which is appropriate todisplay based on a user's eye point; determining a spatial query thatwill render the data according to the eye point; and querying the data,including comparing the spatial query to the index.
 2. The methodaccording to claim 1, wherein the partition structure is a quad-tree. 3.The method according to claim 1, wherein the index is an R-tree.
 4. Themethod according to claim 1, further comprising: storing the partitionstructure as a header file before the data is collected.
 5. The methodaccording to claim 1, further comprising establishing a boundary basedon three-dimensional attributes of the data; and comparing the spatialquery to the boundaries.
 6. A laser system comprising: collecting meansfor collecting point data having three-dimensional coordinates, thecollecting means collecting point data in a regular pattern in twodimensions such that the point data have a regular pattern in twocoordinates; and means for performing the method of claim
 1. 7. Acomputer-readable storage media having computer-executable instructionsstored thereon, wherein when executed performs the method of claim 1.